Process for improving the protective properties of chromium-oxide based compound coatings, by means of stabilization of the chromium ion

ABSTRACT

BY INDUCTIVE EFFECT; - IMMERSING THE COATED MATERIAL INTO THE SAID SOLUTION AT A TEMPERATURE RANGING FROM 30* TO 90*C, for a time ranging from 1&#39;&#39;&#39;&#39; to 15&#39;&#39;, while keeping the solution under constant stirring; - RINSING IN WATER AND DRYING THE SURFACE OF THE COATING.   Wherein: R is a monovalent radical derived from an aromatic type ring, either condensed or not, either containing hetero atoms or not; R&#39;&#39; is a monovalent radical, able to impoverish the electronic density of the enolic group   Process for improving the protecting properties of chromium oxide based coatings, including sequentially the following operations: - PREPARING AN AQUEOUS SOLUTION, WITH CONCENTRATIONS RANGING FROM 0.1 TO 10 G/LITER OF A BETA-DIKETONE WITH THE FOLLOWING GENERAL FORMULA

ijllifitm @TEKQS PHTQTTT 11 5 1 Baudo et a1. Dee. 1Q, 197i 1 PROCESS FORIMPROVING THE chromium oxide based coatings, including sequentiallyPROTECTIVE PROPERTIES OF the following operations: CHROMIUM-OXIIDE BASEDCOMPOUND COATINGS BY MEANS OF preparlng an aqueous solution, w1thconcentratlons ranging from 0.1 to 10 g/liter of a. beta-diketone withSTABILIZATION OF THE CHROMIUM ION the following general formula [75]Inventors: Giuseppe Baudo, Vicenza; Giuseppe Bombara, Rome, both ofItaly [73] Assignee: Centre Sperimentale Metallurgico R S.p.A., Rome,Italy 0=0 c-o1r [22] Filed: July 10, 11972 21 Appl. No.: 270,291

[] Foreign Application Priority Data J1 31,1971 I l 5204271 u y ta yWherein: 52 us. c1 117/62, 117/71 117/127 R is a mmovalem radicalderived from an aromatic 1 30, l ring, either Condensed Or not, either51 1m, (:1 B44d 1M4 containing hetero amms ml; [58] Field oi searchll7/6 2 71 M 127 130 R R is a monovalent radical, able to impoverish the117/621. 204/ 1 6 electronic density of the enolic group [56] ReferencesCited OH UNITED STATES PATENTS 11 3,484,343 12/1969 Kitamura et a1.204/35 R 3,567,599 3/1971 3,615,888 10/1971 3,761,303 9/1973 byinductive effect;

- immersing the coated material into the said solution at a temperatureranging from 30 to C,

Primary Examiner wmiam Martin for a time ranging from 1" to 15, whilekeeping the Assistant Examiner-Janyce A. Bell Solution under constantSurfing;

Attorney, Agent, or FirmYoung & Thompson rinsing in water and drying thesurface of the coating.

[57] ABSTRACT Process for improving the protecting properties of 7Claims, 1 Drawing Figure PATENIE' an: 1 01974 POTENTIAL The presentinvention covers a process and a composition for improving theprotective properties of chromium oxide based compound coatings by meansof stabilization of the chromium ion. More particularly the inventioncoversthe improvement of the protective properties of thin chromiumoxide based coatings, by means of a superficial stabilization processingof the chromium ion, based on the chelating action exerted upon the sameion, by the beta-diketones.

It is known, for example, that the products called Tin-Free Steels,Chromium-Type resulted as the most suitable for the substitution of tinin the tin plate used for food containers. In the herein mentionedproducts, tin is substituted with a thin compound coating ofchromium-chromium oxide (of the order of a few tenths of a micron). Thechromium oxide has the twofold function of sealing the microporositiespresented by the chromium layer which is thin on account of economy andstability, and of supplying a very good anchorage basis for theapplication of protective varnishes or paints.

The object of thepresent invention is precisely improving the sealingaction of chromium oxide upon the microporosities of the coating,increasing, in the same time, the adhesion of the varnish to thesubstratum. In the process, which is the object of the presentinvention, this purpose is fulfilled by means of stabilization of thechromium ion. This stabilization is obtained, on the basis of thepresent invention, by blocking the chromium ions into chelated complexesinsoluble in water, obtained by reaction of the chromium ion with thebeta-diketones corresponding to the general formula:

The complexing action of the beta-diketones determines a decrease of theporosity of the coating which becomes more compact and thereforedevelops a more efficacious protective action.

As it is known, beta-diketones in aqueous solution originate anequilibrium wherein the following tautomeric forms participate (whichforms are distinguishable for the migration of a hydrogen atom from acarbon atom to the adjacent carbon atom):

Since the enolic form II presents an acidic character,

- and since unshared electronic doublets are present on the oxygen atomof the ketonic group in a beta position in respect to the enolic group,the formation of a 6- terms ring, wherein the enolic and ketonic oxygenatoms are bound to the chromium ion, respectively, with a covalent and adonor bond, is possible:

It is advisable now, to emphasize that the nature of the radical R and Rplays a fundamental role in connection with the present invention. Thesubstituting radical R, according to the process which is the object ofthe present invention, is chosen actually, so as to stabilize, as muchas possible, the ring structure (1). This is possible every time R is agroup containing double conjugated bonds with extension, therefore ofthe double bond alternation up to the ketonic group. In this case, infact, resonance structures can be inferred, such as, for example, thefollowing ones in the case where R is a phenyl group:

which stabilizes the chelate structure.

The radical R may be chosen among the monovalent radicals derived fromaromatic type rings, either condensed or not, either containing heteroatoms or not.

In the process, which is the object of the present invention, the choiceof the radical R is effected among the electrons acceptor functionalgroups, the inductive effect of which implies an impoverishment of theelectronic density of the enolic group. In this way, the detachment ofthe proton H bound to it, is favoured, and, therefore, the acidity ofthe enolic group itself is enhanced. In order to realize the importanceof what has been previously said, it is sufficient to remember that, inthis way, the number of beta-ketoenolate ions present in the solution isincreased, with a consequent increase of the formation kinetic of thering (1), and besides, chosing properly the radical R, the production ofbeta-keto-enolate ions in sufficient amounts, for the purposes of thepresent invention, is secured even with slightly acidic or neutral pH.If the R group were not an acidifying group, the production of enolateions would still be possible with alkaline pH, but in these conditions,the chromium oxide would begin to become soluble and thence thetreatment would be less efficacious.

The experience has indicated, as particularly fit for the purpose to beattained, the groups obtained from the methyl radical by partial ortotal substitution of the hydrogen atoms with halogen atoms.

Inc

where R is a monovalent radical, such as the phenyl group C H the thenylgroup C H S, the naphthyl group C H the pyrryl group C H N and the p.fluoro phenyl group C H. ,F. R is a monovalent radical able toimpoverish the electronic density of the enolic group by inductiveeffect, such as the trichloro-methyl group CCl or trifluoro-methyl groupCF heating the solution prepared as hereinbefore described at atemperature ranging from 30 to 90C;

immerging the chromium plated material into the hot solution for a timeranging from 1 sec. to minutes, while keeping the solution understirring;

rinsing with PM) and drying the surface of the coating.

Furthermore, it should be remembered, that in the case where the watersolubility of the chosen betadiketone is low, the present inventionprovides the addition of a nonionic surface active agent in aconcentration up to 1% by weight to the processing solution. Thissurface active agent facilitates the formation of a dispersion.

Now, it should be emphasized that the present invention process is notlimited to the case of the coatings based on chromium-chromium oxide. Infact it can be also applied in all these cases wherein a film ofchromium oxide is used to seal the porosity of any metallic coating.

In order to make clearer the principle of the use and of the operationof the present invention, some illustrative, but not limitativeembodiment examples are supplied with reference to the drawing, which isa plot which shows in the curves a and b the trend of the cur rentdensity of the anodic dissolution of the substratum,

respectively before and after the treatment, as a function of thepotential.

In the drawing the porosity of the coating is measured by means of anelectro-chemical technique, consisting of the determination of thepotentiodynamic anodic curve of the said material in an aggressivemedium. The maximum density of the current of the anodic dissolution ofthe substratum is directly proportional to the degree of the porosity ofthe coating. M is the maximum of the current density of the materialbefore the treatment, M is that of the material after the treatment.

EXAMPLE 1 The material to be treated is a carbon steel (blacksheet-steel) electrolytically coated with a film with the followingcomposition:

Metallic chromium Chromium in the oxide 227 mg/dm 0.596 mg/dm Thismaterial is immerged into an aqueous solution of Z-thenoyltrifiuoroacetone (H T T A), with the following characteristics:

60C 20 g/ liter temperature H T T A concentration EXAMPLE 2 The materialto be treated is a carbon steel (black sheet-steel) electrolyticallycoated with a film with the following composition:

Metallic chromium Chromium in the oxide 3.10 mg/dm 0.11s mg/dm Thismaterial is immerged into an aqueous solution of2-thenoyl-trifluoro-acetone (H T T A) with the followingcharacteristics:

Temperature C H T T A concentration 50 g/liter Nonionic surface activeagent concentration 2 g/liter After a 30 seconds immersion in the saidsolution, under stirring, the material is rinsed.

The untreated material presents a maximum of current density M equal to0.21 mA/cm after the treatment the maximum M is 0.12 mA/cm EXAMPLE 3 Thematerial to be treated is a carbon steel (black steel-sheet)electrolytically coated with a film with the following composition:

Metallic chromium Chromium in the oxide 2.14 mg/dm 0.254 mg/dm Thismaterial is irrunerged in an aqueous solution of 2-furoyltrifiuoroacetone with the following characteristics:

Temperature 80C 2-furoyl-trifluoro acetone concentration g/literNonionic surface active agent concentration 2.5 g/liter.

After a seconds immersion into the solution, under stirring, thematerial is rinsed and dried.

The untreated material present a maximum of current density lVl equal to0.21 mA/cm while after the treatment the maximum M is 0.13 mA/cm Thepresent invention has been described with particular reference to thespecific embodiments thereof, but it is intended that modifications andvariations may be introduced therein, without infringing the protectionlimits of the invention.

What is claimed is:

1. A process for improving the protecting properties of chromium oxidebased coatings, comprising immersing a metal substrate having thereon achromium oxide based coating, in an aqueous solution of 0.1 to 10 gramsper liter of a beta-diketone of the formula in which R is a monovalentaromatic ring-containing radical and R is a monovalent radical able toimpoverish the electronic density of the enolic group by inductiveeffect, at a temperature from 30 to 90C., for 1 second to minutes, withconstant stirring, then 0 rinsing the coated substrate in water anddrying the surface of the coating.

2. A process as claimed in claim 1, in which R is a member selected fromthe group consisting of phenyl, thenyl, furyl, naphthyl, pyrryl andfluoro-phenyl.

3. A process as claimed in claim 1, in which R is a member selected fromthe group consisting of trifluoromethyl and trichloro-methyl.

4. A process as claimed in claim l, in which said solution contains upto 1% by weight of a nonionic surface active agent.

5. A process as claimed in claim 1, in which said substrate is steel.

6. A process as claimed in claim l, in which the ring of R contains atleast one hetero atom.

7. A coated substrate produced by the process of

1. A PROCESS FOR IMPROVING THE PROTECTING PROPERTIES OF CHROMIUM OXIDEBASED COATINGS, COMPRISING IMMERSING A METAL SUBSTRATE HAVING THEREON ACHROMIUM OXIDE BASED COATING, IN AN AQUEOUS SOLUTION OF 0.1 TO 10 GRAMSPER LITER OF A BETA-DIKETONE OF THE FORMULA
 2. A process as claimed inclaim 1, in which R is a member selected from the group consisting ofphenyl, thenyl, furyl, naphthyl, pyrryl and fluoro-phenyl.
 3. A processas claimed in claim 1, in which R'' is a member selected from the groupconsisting of trifluoro-methyl and trichloro-methyl.
 4. A process asclaimed in claim 1, in which said solution contains up to 1% by weightof a nonionic surface active agent.
 5. A process as claimed in claim 1,in which said substrate is steel.
 6. A process as claimed in claim 1, inwhich the ring of R contains at least one hetero atom.
 7. A coatedsubstrate produced by the process of claim 1.